Guest Blogger John Sylla reports on new research showing that changes in pupils may be just as effective as genital measurements in studying sexual orientation

Researchers at Cornell University have found that human pupil dilation differs according to sexual orientation in both men and women.

Straight and gay men’s pupils dilate, or open wider, significantly more when they view stimuli depicting members of their more preferred sex (women for straight men, men for gay men), while bisexual men’s pupils dilate to images of both sexes.

In contrast, straight women responded about evenly to images of men and women. Lesbian women respond much more strongly to images of women, while bisexual women were a middle case whose pupils dilated viewing both sexes but more strongly to images of other women.

The research results, published in the Journal PLoS ONE on August 3, 2012 are consistent with other recent research that used genital probes to measure responses. The authors note that camera-based eye measurements are less intrusive than genital probes, so a broader population might be willing to be measured this way.

In addition, while genital probes are different for men and women because of anatomy, the eye measurement process is identical. Thus, pupil dilation results may be more valid to compare men’s and women’s responses.

Participants, 165 men and 160 women, described their sexual orientations on seven-point scales for identity, attractions, fantasies and infatuations. The sample demographics were not representative of the general population, as the researchers actively recruited bisexual and gay participants.

The results are notable for several reasons. Pupil dilation is an automatic response that does not involve any “choice” about what a person finds attractive. The results support the position that one does not choose his or her sexual orientation.

In addition, the results confirm the existence of bisexual arousal in some men, in agreement with two 2011 studies. Earlier studies using more limited recruiting had not found distinctly bisexual arousal patterns in men, though they conceded that bisexual indentities and behaviors clearly existed.

Gerulf Rieger, the lead author of the pupil dilation study, was himself author of one of the earlier papers calling male bisexuality into question, making the current paper something of a turnabout. As with a 2011 study by Allen Rosenthal finding bisexuality in men, Rieger recruited bisexual participants from internet venues frequented by men indicating an interest in both men and women, rather than from gay and alternative newspaper publications used in his previous study.

The study also lends weight to earlier results finding a physiological bisexual response in most women except lesbians, even if the women are not consciously aware of that response. It is as if straight-identified women’s minds are somehow less conscious of their genital arousal to other women.

The research was funded in part by the American Institute of Bisexuality. The Institute has faced some criticism from bisexual commentators for supporting research by scientists who had doubted male bisexuality. However, in this case the science has been self-correcting based on additional data.

The advent of physical measures of sexual arousal such as genital, pupil and brain responses may raise interesting issues. For example, would it be ethical and perhaps helpful to offer individuals a “test” of their physical, subconscious, automatic and arguably “basic” sexual orientations?

Such tests could prove disturbing to people who don’t get the result they want or whose arousal patterns are not in line with their self-identities.

But, with society becoming more accepting and unafraid of diverse sexual orientations, such tests could help some people, including adolescents, through the sometimes difficult process of coming to terms with sexuality. It could also lead to family acceptance if being gay or bisexual is not a choice but a fundamental, biological part of who they are.

Finally, more than a few activists and commentators have questioned why we can’t just accept people’s attractions without applying labels. There are also different opinions about whether labels like homosexual, bisexual and transsexual aren’t neutral but instead over-clinical or laden with negative baggage. For example, GLAAD’s Media Reference Guide states that “homosexual” is a disfavored term and suggests “gay” or “lesbian” instead.

However, scientific research using precise terminology can lead to greater awareness and understanding, and that research probably requires putting people in categories, even if that involves words that not all participants and commentators want.

— John R. Sylla, J.D., M.B.A., serves on the board of directors of American Institute of Bisexuality (AIB), whose mission is to encourage, support and assist research and education about bisexuality. The PLoS ONE article indicates that AIB had no part in study design, data collection and analysis, decision to publish results or preparation of the manuscript.